The technical sector of the invention concerns the field of power supply methods and devices for powering public lighting networks.
The discharge lamps used for public lighting are conventionally powered by an electrical distribution network through inductive resistors called ballasts. The illumination and power of these lamps are strongly affected by the voltage of the electrical distribution network. Moreover, an unsatisfactory correlation is noted between the needs for high-degree illumination in the evenings when traffic is at its busiest and when energy consumption is at its peak. The network voltage is therefore at its lowest point and the lighting level is at its lowest.
At night during the "low-consumption hours", the network voltage regains its high limit and thus corresponds with the conventional devices used for public lighting at a maximum lighting level when the traffic, the satisfactory lighting of local residents and energy saving involve a reduced lighting level. This results in a significant waste of electric energy.
On the other hand, it is now admitted that the frequency (50 or 60 hertz) of the electric distribution network is too low to ensure maintaining ionization of the electric arc of lamps and which is therefore interrupted and reignited twice per period, namely 100 (or 120) times per second. Reignition is obtained by a voltage peak which provokes ageing of the lamps when the lighting oscillations generate a stroboscopic effect, that is a source of visual fatigue. By feeding the electric arc with a frequency current greater than 5 kilohertz, these drawbacks are eliminated and the lifetime of the lamp is significantly lengthened.
The patent application FR 2,542,152 describes a method and device for powering discharge lamps with frequencies of about 800 hertz to 150 kilohertz by a pseudo-square, trapezoid or square signal delivered by a generator which can be fed with DC by a mounting shown on FIGS. 6 and 7 of this document. Said mounting comprises:
a diode bridge connected to the network supply, PA1 a self-inductive resistor connected to this single polar source by a reversing switch controlled by a control circuit fixing the period of the sequence cycle and the conduction time. The energy stored in the self-inductive resistor is discharged into the output capacitors by passing through a diode. Control of the switching transistor is carried out by a mounting comprising an oscillator, a single vibrator and control transistors. A transistor connected to a circuit equipped with Zenner diodes acts on the conduction time of the switch according to the output voltage and regulates the output voltage so as to compensate the fluctuations of variations of the charge of the network supply voltage. PA1 a device (called "central unit") situated at the connection point of the alternative energy network taking from a network a sinusoidal and in phase current feeding the feed line of the group of lamps by a continuous voltage source galvanically isolated from the network and supplying (injecting) the group of lamps with a fixed power able to be adjusted according to several reference variables, and PA1 devices (called "generators") situated close to each lamp and providing the lamps with a current of medium frequency, that is a frequency of generally between 5 kilohertz and 100 kilohertz and in particular between 15 and 20 kilohertz. PA1 a diode bridge PA1 at least one rectified voltage--DC voltage converter fed by the diode bridge which is a transformer converter, whose output is galvanically isolated from the input and which does not have an automatic control for the output voltage. PA1 the use of a transformer converter (generally known as "fly-back" converter), and PA1 an automatic control of the delivered (or "injected") power to the primary of the transformer, excluding any output automatic control, and PA1 a galvanic isolation between the input and output of the converter. PA1 the device can comprise several rectified voltage converters with identical DC. voltage which can be fed by a common diode bridge and whose outputs are connected in parallel, PA1 in particular, the device can comprise one to four and in particular three diode bridges, and one to twelve and especially three, six or nine converters whose outputs are connected in parallel so as to be used by being fed, for example, by an alternative three-phase network, PA1 said rectified voltage converter with a DC voltage comprises a circuit or an output voltage monitoring circuit or circuit arm (FIG. 9) which comprises a Zenner diode connected in series with a threshold adjustment potentiometer and with the input (and/or the transmitter) of a transducer (or transmitter) whose input is galvanically isolated from the output. The transducer is preferably constituted by an optocoupler. Said circuit or circuit arm is connected to the output terminals of the converter, the threshold voltage of this circuit being slightly more (about 1 to 25% and especially between 5 and 15%) than the normal output voltage of the converter. The output of the transducer, preferably constituted by the receiver of an optocoupler, is connected to the circuit for adjusting the switching frequency of the converter so as to reduce the average power delivered at the output of the converter when the output voltage exceeds a value able to vary during the start up phase for several minutes and predetermined in an established operation, said transducer or optocoupler accordingly being normally inoperative, PA1 the secondary of the transformer is connected to a diode (or to several series diodes), a circuit (or circuit arm) being connected to the terminals of the diode(s) so as to control zero switching of the switch of the converter. The zero switching control circuit comprises to input of the transducer whose output is galvanically isolated from the input and preferably comprises the emitter of an optocoupler whose receiver (output of the transducer) is connected to the switching control circuit of the switch so as to only authorize control circuit of the switch so as to only authorize closing of the switch after cancellation of the current coming out of the secondary of the transformer, PA1 the converter comprises a circuit for controlling switching of the switch (FIG. 8) which comprises means ("clock" means) to adjust the switching frequency of the switch according to a power reference variable to be delivered at the output by keeping constant a conduction time of the switch. The frequency (and/or clock) adjustment means preferably comprise a DC voltage source, several reference voltages representing power reference variables, a current source proportional to the voltage representing the power reference variable, a capacitor, a diac and a constant period timing circuit, PA1 the circuit comprises a circuit for compensating the AC voltage variations of the network feeding the bridge which comprises (FIG. 6), PA1 said converter preferably further comprises: PA1 an input filter for protection against voltage waves, PA1 an anti-rejection lowpass input filter, these filters being placed upstream of the diode bridge. PA1 a converter device according to the invention is selected whose power is adapted to the power normally consumed by the lamps and their associated generators, PA1 the input of said device is connected to an electric network providing an alternative, mono-, bi-, or three-phase voltage source, for example under a voltage of 230 volts and a frequency of 50 hertz, PA1 the generators associated with the lamps are connected in parallel to the output of the device by DC current transport network preferably comprising two insulated wires, PA1 one or several power reference variables are adjusted corresponding to the power normally consumed by the plurality of lamps according to one or several predetermined lighting modes, PA1 the generators are preferably fed by a DC voltage whose potentials with respect to the earth have a neighboring value and opposite sign, PA1 and if required:
This type of AC-DC converter, which is equipped with automatic control regulating the output voltage, has various drawbacks, and in particular owing to the complexity of the automatic control circuits for obtaining a steady, precise and reliable operation and linked with the difficulty to satisfy the standardizing constraints seeking to limit the radiated electromagnetic waves or feeders.
The U.S. Pat. No. 4,630,005 describes an AC-DC converter feeding several AC-DC converters (forming a type of electronic ballast) which each feed one or several discharge lamps. The AC-DC converter consists of a simple mounting of diodes adapted for a three-phase input voltage and to output delivery an AC voltage on three wires.
The U.S. Pat. No. 4,277,728 describes (FIGS. 1 and 2a) a supply system similar to the one described in the Patent FR 2,542,152. The embodiment of the AC-DC converter shown on FIG. 2b of this document uses a transformer whose primary is connected in series to a switching transistor, at the output of a diode bridge equipped with a filter. The output voltage is regulated by changing either the cyclic ratio or the switching frequency. The output voltage, filtered from the harmonic 2 of the network frequency, is used to modify the frequency of the control circuit of the switch so as to keep a constant output voltage. The devices described in this document are adapted to feed a single lamp requiring a weak power, namely several tens of watts.